Magnetoresistive head

ABSTRACT

A magnetoresistive head of a type including a magnetoresistive film arranged between a lower shield layer and an upper shield layer, wherein the lower shield layer has a non-magnetic layer adjacent to it and the lower shield layer and the upper shield layer are formed such that their separation at at least part of a boundary between the lower shield layer and the upper shield layer is larger than their separation in a vicinity of the magnetoresistive film, and an insulating film is arranged between the lower shield layer and the upper shield layer, wherein the lower shield layer and the non-magnetic layer adjacent thereto are formed such that they differ in height and there exists a difference in level at their boundary.

CROSS REFERENCE TO RELATED APPLICATION

This is a continuation of U.S. application Ser. No. 10/200,139, filedJul. 23, 2002. This application relates to and claims priority fromJapanese Patent Application No. 2001-376658, filed on Dec. 11, 2001. Theentirety of the contents and subject matter of all of the above isincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a magnetoresistive head of the type inwhich sensing current is applied in the thickness direction of themagnetoresistive film, a magnetic disk apparatus provided with saidmagnetoresistive head, and a process for production of saidmagnetoresistive head.

2. Description of the Related Art

The magnetic data storage system has been increasing in areal recordingdensity at a surprisingly fast annual rate of 100%. The high recordingdensity requires the magnetic head mounted on the magnetic data storagesystem to have a higher output, a narrower track width, and a narrowershield-to-shield distance.

The object of increasing output is achieved by improving the performanceof the magnetoresistive film. For recording densities up to severalgigabits per square inch, an anisotropic magnetoresistive (AMR) film hasbeen used. However, for recording densities higher than that, a giantmagnetoresistive (GMR) film is being used now. The magnetoresistive filmof next generation for GMR film includes the tunneling magnetoresistive(TMR) film (mentioned in Journal of Magnetism and Magnetic Materials,vol. 139, 1995, pp. L231-L234) and CPP (current perpendicular to theplane)-GMR film (mentioned in Journal of Applied Physics, vol. 89, 2001,pp. 6943-6945) in which current is applied in the directionperpendicular to the plane of the GMR film.

For reduction of track width, attempts are being made to develop a newexposure technology using a lithography apparatus equipped with a lightsource for shorter wavelength and to develop a new image enhancementtechnique. Possibility of further reduction in track width (smaller thana quarter micron or even a tenth of micron) is being investigated.

The object of reducing the shield-to-shield distance is hard to achievefor the GMR film of CIP (current into the plane) structure, in whichsensing current flows into the plane of the magnetoresistive film. ForCIP-GMR head, thin insulating gap films are provided between the shieldfilm and the GMR film, and between the shield film and the electrodefilm to supply sensing current to the GMR film. Such a thin insulatinggap film permits sensing current to leak to the shield film. In order toavoid this shortcoming, an idea of keeping the insulating gap film thickexcept for the read track part is disclosed in Japanese Patent Laid-openNos. 111248/1994 and 111008/1996.

By contrast, the object of reducing the shield-to-shield distance iseasy to achieve for the GMR film of CPP structure (in which sensingcurrent flows in the direction perpendicular to the plane of themagnetoresistive film). CPP structure needs no insulating gap filmunlike that of CIP structure. A magnetic head equipped with a TMR film(which is a magnetoresistive film of CPP structure) is disclosed inJapanese Patent Laid-open No. 213351/1999. According to this disclosure,the object of reducing the shield-to-shield distance is achieved byarranging a TMR element in the pedestal region formed in the upper andlower shields.

The disadvantageous technology (Japanese Patent Laid-open No.213351/1999) mentions that it is necessary to form the pedestal regionin the upper and lower shields in order to reduce the shield-to-shielddistance in the case where a TMR film is used. In practice, however, itis also necessary to consider other structure than the read track forpractical head structure.

To be concrete, in the production of a magnetoresistive head of CPPstructure, it is important to pattern the magnetoresistive film into adesired shape without damage and to suppress leakage of sensing currentacross the upper and lower shields used as the electrodes.

OBJECT AND SUMMARY OF THE INVENTION

It is an object of the present invention to provide a magnetoresistivehead of CPP structure with a magnetoresistive film of CPP type,including TMR film as well as CPP-GMR film, said magnetoresistive headbeing less liable to damage during patterning and having a high outputand no leakage current across the upper and lower shields. It is anotherobject of the present invention to provide a magnetic disk apparatusprovided with said magnetoresistive head. It is further another objectof the present invention to provide a process for producing saidmagnetoresistive head in high yields.

The present invention is directed to a magnetoresistive head of the typehaving a magnetoresistive film arranged between the lower shield layerand the upper shield layer, a pair of electrodes to apply sensingcurrent in the thickness direction of said magnetoresistive film, and adetecting means to detect the change in resistance which saidmagnetoresistive film makes as the external magnetic field changes,wherein said lower shield layer has a non-magnetic layer adjacent to itand said non-magnetic film is separate from said lower shield layer by aboundary at least part of which is covered with an insulating protectivefilm.

The present invention is directed also to a process for producing amagnetoresistive head having a magnetoresistive film arranged betweenthe lower shield layer and the upper shield layer and a pair ofelectrodes to apply sensing current in the thickness direction of saidmagnetoresistive film, said process comprising a step of forming a lowershield layer on a substrate, a step of patterning said lower shieldlayer, a step of forming a non-magnetic film over the entire surface ofthe substrate, a step of planarizing said lower shield layer and saidnon-magnetic film such that they are approximately equal in thickness, astep of covering at least part of the boundary between said lower shieldlayer and said non-magnetic film, a step of forming a magnetoresistivefilm over the entire surface of the substrate, a step of patterning saidmagnetoresistive film, a step of covering with an insulating film atleast part of the side wall formed by patterning said magnetoresistivefilm, and a step of forming the upper shield layer.

Other and further objects, features and advantages of the invention willappear more fully from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing the step of patterning themagnetoresistive film in the magnetoresistive head of CPP structurepertaining to one embodiment of the present invention.

FIGS. 2A to 2C are schematic diagrams showing the steps of patterningthe magnetoresistive film in the disadvantageous magnetoresistive headof CIP structure.

FIGS. 3A to 3D are schematic diagrams showing the steps of patterningthe magnetoresistive film in the conventional magnetoresistive head ofCPP structure.

FIG. 4 is a schematic diagram showing the step of patterning themagnetoresistive film in the magnetoresistive head of CPP structurepertaining to another embodiment of the present invention.

FIGS. 5A and 5B are schematic diagrams showing the steps of patterningthe magnetoresistive film in a disadvantageous magnetoresistive head ofCPP structure. FIG. 5C is a schematic diagram showing the structure ofthe air bearing surface of the magnetoresistive head. FIG. 5D is asectional side view of the magnetoresistive head.

FIGS. 6A and 6B are schematic diagrams showing the steps of patterningthe magnetoresistive film in the magnetoresistive head of CPP structurepertaining to one embodiment of the present invention. FIG. 6C is aschematic diagram showing the structure of the air bearing surface ofthe magnetoresistive head. FIG. 6D is a sectional side view of themagnetoresistive head.

FIGS. 7A and 7B are schematic diagrams showing the steps of patterningthe magnetoresistive film in another disadvantageous magnetoresistivehead of CPP structure. FIG. 7C is a schematic diagram showing thestructure of the air bearing surface of the magnetoresistive head. FIG.7D is a sectional side view of the magnetoresistive head.

FIGS. 8A and 8B are schematic diagrams showing the steps of patterningthe magnetoresistive film in the magnetoresistive head of CPP structurepertaining to another embodiment of the present invention. FIG. 8C is aschematic diagram showing the structure of the air bearing surface ofthe magnetoresistive head. FIG. 8D is a sectional side view of themagnetoresistive head.

FIG. 9 is a top view of a disadvantageous magnetoresistive head of CPPstructure.

FIG. 10 is a top view of another disadvantageous magnetoresistive headof CPP structure.

FIG. 11 is a top view of a disadvantageous magnetoresistive head of CPPstructure.

FIG. 12 is a top view of a disadvantageous magnetoresistive head of CPPstructure pertaining to one embodiment of the present invention.

FIG. 13 is a top view of a disadvantageous magnetoresistive head of CPPstructure pertaining to another embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In what follows, the invention will be described in more detail withreference to the accompanying drawings.

First, a mention is made of the difference in structure between themagnetoresistive head of CIP structure and the magnetoresistive head ofCPP structure. This difference, which suggested the present invention,will be explained with reference to FIGS. 1 to 4.

In the case of a disadvantageous magnetoresistive head of CIP structure,the magnetoresistive film is patterned by etching steps shown in FIG. 2.First, a substrate (not shown) of alumina-titanium carbide (Al₂O₃.TiC)is coated with an insulating material such as alumina. On thisinsulating material are arranged a lower shield layer 10 and aninsulating film 11 of non-magnetic material such that the former is heldbetween the latter. They have an approximately equal thickness. On thelower shield layer 10 and the insulating film 11 is formed a lower gaplayer 12 of insulating material. On the lower gap layer 12 is formed themagnetoresistive film 131 which is a metal multi-layered film. On themagnetoresistive film 131 is formed a resist mask 14 which defines thetrack width of the magnetoresistive film 131. (See FIG. 2A.) Themagnetoresistive film 131 undergoes etching by plasma process such asion milling, so that a desired pattern is formed. Ideally, this plasmaprocess is intended to neutralize accelerated ions from the plasmasource and perform etching with electrically neutral atoms (such as Ar).In practice, however, due to difficulties in electrically neutralizingall ions completely, some ions (such as Ar⁺) are applied to etchedsubstance. In the intermediate stage of etching shown in FIG. 2B, thecharge of ions impinging upon the magnetoresistive film 131 escapesthrough the substrate holder of the etching apparatus from the edge ofthe substrate, because the magnetoresistive film 131 extendscontinuously on the entire surface of the substrate. In the final stageof etching, shown in FIG. 2C, in which etching proceeds to such anextent that that part of the magnetoresistive film 131 which is notcovered by the resist mask 14 is removed, atoms and ions generating fromthe plasma source impinge upon the lower gap layer 12 of insulatingmaterial. In this state, there exists no localized charge because thelower shield layer (which is made of metallic material) is not exposedon the surface of the substrate.

By contrast, in the case of a disadvantageous magnetoresistive head ofCPP structure, the magnetoresistive film is patterned by etching stepsshown in FIG. 3. The CPP structure is identical to the CIP structure inthat both have the lower shield layer 10 and the non-magnetic insulatingfilm 11 arranged adjacent to the former. However, the CPP structurediffers from the CIP structure in that the former has themagnetoresistive film 132 placed directly on the lower shield layer 10and the non-magnetic insulating film 11. In the intermediate stage ofetching shown in FIG. 3B, the charge of unneutralized ions impingingupon the magnetoresistive film 132 escapes through the substrate holderof the etching apparatus from the edge of the substrate, because themagnetoresistive film 132 still covers the entire surface of thesubstrate. However, in the stage of etching shown in FIG. 3C, in whichthe magnetoresistive film 132 has been removed completely by etching,the lower shield layer 10 of metallic material is exposed on the surfaceof the substrate and is electrically isolated by the adjacent insulatingfilm 11. Therefore, the charge of ions accumulates on the lower shieldlayer 10. This charge causes damage to the magnetoresistive film 132.This damage is more serious as the surface of the ion-irradiated metalfilm increases, on account of the antenna effect which collects charges.

In order to prevent damage due to ion irradiation at the time ofetching, it is essential to neutralize ions completely. In practice,however, it is difficult to neutralize all of the ions evolved from theplasma source. An alternative way to prevent damage is to modify thehead structure. This object has been achieved by the present invention.

According to the present invention, the magnetoresistive head ismodified as follows.

A difference in level at the boundary between the lower shield layer andthe non-magnetic film is tolerated.

The insulating protective film is formed such that the distance betweenthe lower shield layer and the upper shield layer (measured at at leastpart of the boundary between the lower shield layer and the non-magneticfilm adjacent to it) is larger than the distance between the lowershield layer and the upper shield layer (measured in the vicinity of themagnetoresistive film). Moreover, an insulating film is formed betweenthe lower shield layer and the upper shield layer.

The vicinity of the magnetoresistive film is a range within 60 nm fromboth sides of the narrowest part of the magnetoresistive film.

The present invention is directed also to a magnetoresistive head of thetype having a magnetoresistive film arranged between the lower shieldlayer and the upper shield layer, a pair of electrodes to apply sensingcurrent in the thickness direction of said magnetoresistive film, and adetecting means to detect the change in resistance which saidmagnetoresistive film makes as the external magnetic field changes,wherein said lower shield layer is provided with an insulatingprotective film at the part except for the part on which themagnetoresistive film is arranged.

The above-mentioned magnetoresistive head is modified such that theinsulating protective film is so formed as to cover that part on thelower shield layer which excludes the part on which the magnetoresistivefilm is arranged and at least part of the boundary between the lowershield layer and the non-magnetic film adjacent thereto.

According to the present invention, the above-mentioned process forproducing the magnetoresistive head is modified as follows:

The step of planarizing is accomplished by mechanical polishing orchemical mechanical polishing.

The step of planarizing is accomplished by any of plasma etching,sputter etching, ion milling, and reactive ion etching.

The above-mentioned embodiments proved that the process of the presentinvention gives high-output magnetoresistive heads in high yields whichare only little liable to damage at the time of patterning and are freeof current leakage across the upper and lower shield. The presentinvention covers also a magnetic data storage system in which theabove-mentioned magnetoresistive head is used as the read head. Themagnetic data storage system has a limited leakage of sensing current.

The example of the present invention will be described in more detailwith reference to FIG. 1. FIG. 1 shows a stage in which etching hascompletely removed that part of the magnetoresistive film 132 which isnot covered by the resist mask 14. It is to be noted that the insulatingprotective film 20 covers at least part of the boundary between thelower shield layer 10 and the non-magnetic insulating film 11 adjacentthereto and also covers that part on which the magnetoresistive film isnot arranged. The thus formed insulating protective film 20 minimizesthe area of the lower shield layer 10 which is exposed on the substratesurface after etching of the magnetoresistive film 132 has beencompleted. In this way it is possible to reduce the amount of chargeaccumulating on the lower shield 10.

In the above-mentioned example, the insulating protective film 20produces a remarkable effect of improving yields up to 98% (yields incomparative examples are almost zero). Incidentally, the formation ofthe insulating protective film 20 can be confirmed by observing (with anSEM) the air bearing surface or by observing cross sectional structurealong the element height direction.

It is also possible to reduce damage due to ion milling if another coveris formed on that part of the lower shield 10 on which themagnetoresistive film is not arranged.

It was found that the present invention produces its effect when themagnetoresistive film 132 is either tunneling magnetoresistive film orCPP-GMR film. It was also found that the present invention produces itseffect not only in the case where the magnetoresistive film is etched ina trapezoidal form (as shown in FIG. 1) but also in the case where themagnetoresistive film is etched in a stepped trapezoidal form (as shownin FIG. 4).

The present invention may be applied, without loss of its essentialeffect, to other magnetoresistive film than that of CPP structurementioned above or to etching in other shape than that mentioned above.Such magnetoresistive film includes semiconducting ferromagnetic filmand half-metallic sensing film which would have a high magnetoresistivecoefficient due to its 100% polarity.

Other examples of the present invention will be explained with referenceto FIGS. 5 and 6. The structure mentioned in the following is effectivewhen the distance between the lower shield layer and the upper shieldlayer is reduced. The lower shield layer 10 and an insulating layer 11which is an example of the non-magnetic film adjacent thereto undergochemical mechanical polishing (CMP) so that they have the same height.This planarizing process permits accurate photolithography and finepatterning. Despite this planarizing process, there might occur adifference in level (about 50-100 nm high) at the boundary as shown inFIG. 5A because of difference in etching rate between the lower shieldlayer 10 (which is composed of metallic material) and the insulatinglayer 11 adjacent thereto. This difference in level will cause a seriousproblem in view of the fact that the distance between the upper andlower shield layers will be smaller than 100 nm (or even smaller than 50nm as the recording density increases more in the future). Moreover, theinterlayer insulating film between the upper and lower shield layerswill be as thin as 100 nm in the head of CPP structure. Preventingleakage of sensing current and ensuring sufficient dielectric strengthin this state are deeply concerned with the difference in level at theboundary between the lower shield layer 10 and the insulating layer 11adjacent thereto. This problem is properly addressed in the example ofthe present invention as explained in the following.

First, problems involved in the conventional technology are explainedwith reference to FIG. 5.

Etching starts when the process has proceeded to the stage shown in FIG.5A. This etching removes that part of the magnetoresistive film 132which is not covered by the resist mask 14. Slight over-etching iscarried out intentionally in consideration of the different etching ratewithin the substrate and the process stability. Etching in this mannerpartly removes that part of the lower shield layer 10 which is notcovered by the resist mask 14, as shown in FIG. 5B. Usually, the lowershield layer 10 is etched faster than the insulating layer 11, whichresults in a larger difference in level at the boundary between them.Subsequently, on the lower shield layer 10 and the insulating layer 11are formed the shield interlayer insulating film 15, the longitudinalbiasing layer 16, and the upper shield layer 17. The structure of theselayers, as viewed from the air bearing surface, is shown in FIG. 5C. Itshould be noted that the shield interlayer insulating film 15 (betweenthe lower shield layer 10 and the upper shield layer 17) is thin at theboundary between the lower shield layer 10 and the insulating layer 11.The thinned insulating film 15 tends to cause leakage of sensing currentor breakdown. FIG. 5D is a cross sectional view in the direction ofelement height along the plane containing the longitudinal biasing layer16. Leakage of sensing current tends to occur at the part (deep in thedirection of element height) where the space between the lower and uppershield layers (10 and 17) is small.

FIG. 6 shows the structure pertaining to the present invention, in whichthe problems mentioned with reference to FIG. 5 are addressed. To beconcrete, the structure in FIG. 6 differs from the structure in FIG. 5in that the insulating protective film 20 is so formed as to cover theboundary between the lower shield layer 10 and the insulating film 11adjacent thereto. As noted in FIGS. 6C and 6D, the insulating filmbetween the lower shield layer 10 and the upper shield layer 17 is sothick that there hardly is the possibility of sensing current leakageand breakdown. Incidentally, the insulating protective film 20 shouldpreferably be arranged as broadly as possible and as close to themagnetoresistive film 132 as possible. In practice, the insulatingprotective film 20 may extent to the point about 60 nm off the end ofthe magnetoresistive film in consideration of the accuracy oflayer-to-layer alignment in lithography. In FIG. 6C, the upper shieldlayer 17 constitutes part of the upper electrode and the lower shieldlayer 10 constitutes part of the lower electrode. In addition, the upperand lower shield layers are connected to the power supply and the meansto detect resistance changes as shown in FIG. 6C.

Incidentally, in the case where the magnetoresistive film 132 ispatterned in a stepped trapezoidal shape as shown in FIG. 7, currentleakage tends to occur at the narrow part between the lower shield layer10 and the upper shield layer 17. This problem is solved by arrangingthe insulating protective film 20 as shown in FIG. 8.

A magnetic disk apparatus with a high transfer rate needs a head with areduced capacitance C. If a head of CPP structure is to meet thisrequirement, it is necessary to reduce the shield size further. FIGS. 9and 10 are the top views of the head in which the shield layer has areduced area. It should be noted that the longitudinal biasing layer 16is formed on the boundary between the lower shield layer 10 and thenon-magnetic insulating film 11 adjacent thereto. FIG. 11 is a crosssectional view taken along the line A-A′ in FIG. 9. It should be notedthat the space between the lower shield layer 10 and the longitudinalbiasing layer 16 is small and the space between the longitudinal biasinglayer 16 and the upper shield layer 17 is also small. This situationcauses leakage of sensing current more easily than the situation shownin FIG. 5 or FIG. 7. In this case, a great improvement is made byproving the insulating protective film 20 as shown in FIG. 12. FIG. 13is a sectional view taken along the line B-B′ in FIG. 10. In this case,too, a great improvement is made by providing the insulating protectivefilm 20 as shown in FIG. 13.

Another embodiment of the present invention demonstrated that themagnetoresistive head of improved structure in the above-mentionedexample finds use as the read head for the magnetic disk unit withlimited sensing current leakage.

According to the present invention, the magnetoresistive headillustrated in the above-mentioned example is produced by the processwhich consists of a step of forming a lower shield layer on a substrate,a step of patterning said lower shield layer, a step of forming anon-magnetic film over the entire surface of the substrate, a step ofplanarizing said lower shield layer and said non-magnetic film such thatthey are approximately equal in thickness, a step of covering at leastpart of the boundary between said lower shield layer and saidnon-magnetic film, a step of forming a magnetoresistive film over theentire surface of the substrate, a step of patterning saidmagnetoresistive film, a step of covering with an insulating film atleast part of the side wall formed by patterning said magnetoresistivefilm, and a step of forming the upper shield layer. Planarizing iseffectively accomplished by mechanical polishing or chemical mechanicalpolishing. Planarizing is accomplished also by any of plasma etching,sputtering, ion milling, and reactive ion etching.

According to the present invention, it is possible to produce amagnetoresistive head of CPP structure having a TMR film or a CPP-GMRfilm as the magnetoresistive film. The production process minimizes thedamage that occurs when the magnetoresistive film is patterned and alsoprevents leakage of sensing current and breakdown across the lowershield layer and the upper shield layer. This contributes to productionof high-output magnetoresistive heads in high yields. In addition,according to the present invention, it is possible to produce themagnetic disk apparatus with limited sensing current leakage.

The foregoing invention has been described in terms of preferredembodiments. However, those skilled, in the art will recognize that manyvariations of such embodiments exist. Such variations are intended to bewithin the scope of the present invention and the appended claims.

1. A magnetoresistive head of a type comprising a magnetoresistive filmarranged between a lower shield layer and an upper shield layer, whereinthe lower shield layer has a non-magnetic layer adjacent to it and thelower shield layer and the upper shield layer are formed such that theirseparation at at least part of a boundary between the lower shield layerand the upper shield layer is larger than their separation in a vicinityof the magnetoresistive film, and an insulating film is arranged betweenthe lower shield layer and the upper shield layer, wherein the lowershield layer and the non-magnetic layer adjacent thereto are formed suchthat they differ in height and there exists a difference in level attheir boundary.
 2. The magnetoresistive head as defined in claim 1,comprising an insulating protective film to at least partially providethe larger space, wherein the insulating protective film only covers aportion of the lower shield layer, and the magnetoresistive headcomprising a secondary insulating protective film covering a secondaryportion of the lower shield layer.
 3. A magnetic data storage systemwhich has the magnetoresistive head defined in claim
 1. 4. Themagnetoresistive head as defined in claim 1, comprising a detectingmeans to detect a change in resistance which the magnetoresistive filmmakes as an external magnetic field changes.
 5. The magneto resistivehead as defined in claim 1, comprising a longitudinal biasing layer isprovided at both sides of the magnetoresistive film, and the insulatingfilm is provided on a part of the lower shield layer not having themagnetoresistive film thereon, wherein a portion of the insulating filmis provided under a portion of the longitudinal biasing layer.